Lectures 12 & 13: Anatomy andPhysiology of Skeletal Muscle•Martini et al. Mods 9.1-9.14, pp. 307-333•Universal characteristics of muscle tissue•Microscopic anatomy of skeletal muscle: themuscle fiber, myofilaments, striations•Structure and function at the neuromuscularjunction•The sliding filament theory of muscle contraction•Behavior of whole muscles
Universal Characteristics of Muscle•Responsiveness (excitability):Chemical signals, stretch,other stimuli produce electrical changes across the plasmamembrane•Conductivity:Local electrical change triggers a wave ofexcitation that travels along the muscle fiber•Contractility:Shortens when stimulated to exert force ontissues and organs and to create movement•Extensibility:Capable of being stretched betweencontractions•Elasticity:Returns to its original resting length after beingstretched
___?___Muscle(a)Muscle cellsNuclei(b)•___?___muscle: Lacks striationsand isinvoluntary•___?___muscle—forms layers of digestive, respiratory, andurinary tract: propels contents through an organ, regulatesdiameter of blood vessels
___?___Muscle•___?___muscle:Limited to theheart•Striated and involuntary(a)(b)GlycogenStriationsIntercalated discs
___?___Muscle•___?___muscle: made of long, thread-like cells withmultiple nuclei calledmuscle fibers•Most attach to bone via tendons•Striations—alternating dark and light bands from overlap ofcontractile proteins•Voluntary(a)StriationsMuscle fiber(b)Nuclei
Sarcoplasm:cytoplasm of a muscle fiberSarcolemma:plasma membrane of a muscle fiberSarcoplasmic reticulum:smooth ERthat forms a network around eachmyofibril and stores the calciumthat activates the musclecontraction processMitochondriaMyofibrils:longprotein bundles thatoccupy the mainportion of thesarcoplasmMyofilamentsA bandI bandZ discNucleusMusclefiberThe Muscle Fiber = The Muscle CELLProtein Molecules < Myofilament < Myofibril < Muscle Fiber
(a)Myosin moleculeHead(b)Thick filamentMyosin headMyofilaments•Thick filaments: made of several hundredmyosinmolecules•Thin filaments:actin,tropomyosin, andtroponinmolecules•Elastic filaments:titin (huge, springy protein thatprevents overstretching)Tail
Myofilaments•Contractile proteins—myosinandactindo the work•Regulatory proteins—tropomyosinandtroponin–Like a switch that determines when the fiber can contract andwhen it cannot–Contraction activated by release ofcalciuminto sarcoplasm andits binding totroponin(b)Thick filamentMyosin head(c)Thin filamentTroponin complexG actinTropomyosin
Striations•Myosinandactinare proteins that occur in all cells•Organized in a precise way in skeletal and cardiac muscle–A (anisotropic) band:dArk, particularly where thick and thinfilaments overlap–I (isotropic) band:alternating lIghter band–Z disc:provides anchorage for thin filaments and elastic filamentsSarcomereI bandI bandA bandThick filamentThin filamentElastic filamentZ discZ disc
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muscle tension, Physiology of Skeletal Muscle
